1. Field of the Invention
The present invention relates to a compressor and, more particularly, to an apparatus and method for controlling an operation of a reciprocating compressor.
2. Description of the Prior Art
In general, a reciprocating compressor does not employ a crank shaft for converting a rotational motion to a linear motion, so it has higher compression efficiency than a general compressor.
When the reciprocating compressor is used for a refrigerator or an air-conditioner, a compression ratio of the reciprocating compressor can be varied by varying a stroke voltage inputted to the reciprocating compressor in order to control cooling capacity.
A conventional reciprocating compressor will now be described with reference to FIG. 1.
FIG. 1 is a block diagram showing the construction of an apparatus for controlling an operation of a reciprocating compressor in accordance with a prior art.
As shown in FIG. 1, a conventional apparatus for controlling an operation of a reciprocating compressor includes: a current detector 4 for detecting a current applied to a motor (not shown) of a reciprocating compressor 6; a voltage detector 3 for detecting a voltage applied to the motor; a stroke calculator 5 for calculating a stroke estimate value of the compressor based on the detected current and voltage values and a parameter of the motor; a comparator 1 for comparing the calculated stroke estimate value and a pre-set stroke reference value and outputting a different value according to the comparison result; and a stroke controller 2 for controlling an operation (stroke) of the compressor 6 by varying a voltage applied to the motor according to the difference value.
The apparatus for controlling an operation of the reciprocating compressor operates as follows.
First, the current detector 4 detects a current applied to the motor of the compressor 6 and outputs the detected current value to the stroke calculator 5. At this time, the voltage detector 3 detects a voltage applied to the motor and outputs the detected voltage value to the stroke calculator 5.
The stroke calculator 5 calculates a stroke estimate value (X) of the compressor by substituting the detected current and voltage values and a parameter of the motor to equation (1) shown below and applies the obtained stroke estimate value (X) to the comparator 1.
                    X        =                              1            α                    ⁢                      ∫                                          (                                                      V                    M                                    -                  Ri                  -                                      L                    ⁢                                          i                      _                                                                      )                            ⁢                              ⅆ                t                                                                        (        1        )            wherein ‘R’ is a motor resistance value, ‘L’ is a motor inductance value, a is a motor constant value, VM is a value of a voltage applied to the motor, ‘i’ is a value of a current applied to the motor, and ‘ī’ is a time change rate of the current applied to the motor. Namely, ‘ī’ is a differentiated value of ‘i’ (di/dt).
The comparator 1 compares the stroke estimate value with the stroke reference value and applies a difference value according to the comparison result to the stroke controller 2.
The stroke controller 2 controls the stroke of the compressor 6 by varying a voltage applied to the motor of the compressor 6 based on the difference value. This will be described with reference to FIG. 2.
FIG. 2 is a flow chart of a method for controlling an operation of the reciprocating compressor in accordance with the prior art.
First, when the stroke calculate 5 applies the stroke estimate value to the comparator 1 (step S1), the comparator 1 compares the stroke estimate value with the pre-set stroke reference value (step S2) and outputs a difference value according to the comparison result to the stroke controller 2.
If the stroke estimate value is smaller than the stroke reference value, the stroke controller 2 increases a voltage applied to the motor to control the stroke of the compressor (step S3). If, however, the stroke estimate value is greater than the stroke reference value, the stroke controller 2 reduces the voltage applied to the motor (step S4).
Thus, in the conventional apparatus and method for controlling an operation of the reciprocating compressor, even though a mechanical resonance frequency of the compressor is varied because of the change in the voltage applied to the motor of the compressor based on the stroke estimate value an the stroke reference value, the reciprocating compressor is operated with the always same operation frequency, causing a problem that operation efficiency of the reciprocating compressor deteriorates.
A reciprocating compressor in accordance with a different embodiment of the present invention is disclosed in U.S. Pat. No. 6,644,943 issued on Nov. 11, 2003.